A COMPARATIVE STUDY BETWEEN Pistia stratiotes L. AND ...

A COMPARATIVE STUDY BETWEEN

Pistia stratiotes L. AND Salvinia molesta Mitch.

BASED ON LIFE CYCLE AND SALINITY

TOLERANCE

SITI NORASIKIN BINTI ISMAIL

UNIVERSITI SAINS MALAYSIA

2014

i

A COMPARATIVE STUDY BETWEEN

Pistia stratiotes L. AND Salvinia molesta Mitch.

BASED ON LIFE CYCLE AND SALINITY

TOLERANCE

by

SITI NORASIKIN BINTI ISMAIL

Thesis submitted in fulfilment of the requirement for the Degree of

Master of Science

AUGUST 2014

ii

ACKNOWLEDGEMENTS

I would like to say Alhamdulillah to Allah for giving me the strength and

make me be able to complete my Master of Science from School of Biological

Sciences, Universiti Sains Malaysia. For my beloved mom and dad who always

support and believe in me throughout my study sessions, thank you so much for

being there for me.

My main supervisor, Profesor Mashhor Bin Mansor and wife for always encourage

and guide me in completing my thesis. He is one of the best teachers for me, not only

in pursuing study but the whole life manners. Dr. Asyraf Bin Mansor, my co-

supervisor, thank you for being there and giving your opinion on my study and thesis

writing. Your critics on my thesis really work me out.

To all School of Biological Sciences staffs, especially Mr. Rashid, Mr Khairuddin,

Mr Abdullah and many more for your assistance and helps throughout my project

was conducted. To all my friends, Muzzalifah, Aziera, Nadhirah, Fikri, Nadia,

Nazifah, Reen, Truyen and Aisyah thank you for being there for me and sharing the

information together.

I would like to express my gratitude to Ministry of Higher Education, Malaysia for

sponsoring my study fees under MyMaster Sponsorship Program with the reference

number KPT (B) 891023025254 from 1 May 2012 until 30 April 2014.

Thank you!

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TABLE OF CONTENTS

ACKNOWLEDGEMENTS ii

TABLE OF CONTENTS iii

LIST OF TABLES vi

LIST OF FIGURES vii

LIST OF PLATES ix

LIST OF SYMBOLS AND ABBREVIATIONS x

ABSTRAK xi

ABSTRACT xiii

CHAPTER 1: GENERAL INTRODUCTION 1

1.1 Introduction 1

1.2 Objectives of Study 4

CHAPTER 2: LITERATURE REVIEW 5

2.1 Aquatic Plants 6

2.1.1 The Benefits of Aquatic Plant 8

2.1.2 Problems Rises from Excessive Aquatic Plant 9

2.2 Studied Plants 15

2.2.1 Pistia stratiotes 15

2.2.2 Salvinia molesta 20

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CHAPTER 3: THE LIFE CYCLE OF Pistia stratiotes AND Salvinia molesta 24

3.1 Introduction 24

3.2 Materials and Methods 27



3.3 Results 29



3.4 Discussion 39



3.5 Conclusion 43

CHAPTER 4: COMPETITION BETWEEN Pistia stratiotes AND 44

Salvinia molesta

4.1 Introduction 44


4.3 Results 49

4.4 Discussion 55

4.5 Conclusion 56

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CHAPTER 5: PHYSIOLOGICAL RESPONSES OF Pistia stratiotes AND 57

Salvinia molesta TOWARDS SALINITY

5.1 Introduction 57


5.3 Results 63



5.4 Discussion 73

5.5 Conclusion 76

CHAPTER 6: GENERAL DISCUSSION 77

CHAPTER 7: CONCLUSION 81

REFERENCES 83

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LIST OF TABLES

Table 4.1 Total area of coverage in container A by Pistia stratiotes and 54

Salvinia molesta for eight weeks

Table 4.2 Relative Growth Rate of Pistia stratiotes and Salvinia molesta 54

in 30 days

Table 5.1 List of treatments 60

Table 5.2 The percentage dilution of seawater 61

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LIST OF FIGURES

Figure 2.1 The three primary zones of a lake 7

Figure 2.2 Illustration of Pistia stratiotes 16

Figure 2.3 Phytogeographic highlight of Pistia stratiotes L. in the world map 19

Figure 2.4 Illustration of Salvinia molesta 21

Figure 2.5 Countries where Salvinia molesta has been a serious problem in 23

the fresh water systems

Figure 3.1 Sexual reproduction cycle of Pistia stratiotes 30

Figure 3.2 Vegetative reproduction cycle of Pistia stratiotes 35

Figure 3.3 Vegetative reproduction cycle of Salvinia molesta 37

Figure 4.1 Mean leaves length (cm) of Pistia stratiotes and Salvinia molesta 49

Figure 4.2 Mean leaves width (cm) of Pistia stratiotes and Salvinia molesta 50

Figure 4.3 Mean number of leaves of Pistia stratiotes and Salvinia molesta 51

Figure 4.4 Area of coverage by Salvinia molesta (white) versus 53

Pistia stratiotes (green)

Figure 5.1 Monsoon of Malaysia 59

Figure 5.2 Mean fresh weight of SW1 Treatment for Pistia stratiotes 63



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Figure 5.7 Mean Relative Growth Rates (RGR, day-1

) for all treatments 67

for Pistia stratiotes

Figure 5.8 Mean fresh weight of SW1 Treatment for Salvinia molesta 68





Figure 5.13 Mean Relative Growth Rates (RGR, day-1

) for all treatments 72

of Salvinia molesta

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LIST OF PLATES

Plate 2.1 Inflorescence of Pistia stratiotes (in the red circle) 16

Plate 2.2 Cage like structure of Salvinia molesta papillae (in the red circle) 21

Plate 3.1 The successful germinated seeds 29

Plate 3.2 Enclosed male flower part of Pistia stratiotes 32

Plate 3.3 Opened spathe exposing male and female part of Pistia stratiotes 32

Plate 3.4 Fruit will be produced after a successful fertilization of 32

Pistia stratiotes

Plate 3.5 Pistia stratiotes fruit is bearing seeds 33

Plate 3.6 Seeds of Pistia stratiotes are released from the fruit into water 33

body and then settle down in the soil

Plate 3.7 The sporocarps of Salvinia molesta present among the root-like 38

filaments contain non-viable spores

Plate 3.8 The rhizome of Salvinia molesta (root like filaments) 38

Plate 3.9 Apical bud present at the end of the rhizome of Salvinia molesta 38

x

LIST OF SYMBOLS AND ABBREVIATIONS

C = Degree Celsius

cm = centimetres

Dw = dry weight

g = gram

L = liter

m = metres

m2 = metres squared

m3 = metres cube

mm = millimetres

ppt = parts per thousand

RGR = Relative Growth Rate

t = times

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SATU KAJIAN PERBANDINGAN ANTARA Pistia stratiotes L. DAN Salvinia

molesta MITCH. BERDASARKAN KITAR HIDUP DAN TOLERAN

TERHADAP SALINITI

ABSTRAK

Matlamat kajian ini ialah untuk mengkaji persaingan di antara dua tumbuhan rumpai air

terapung; Pistia stratiotes dan Salvinia molesta yang tersenarai di dalam kumpulan

rumpai air noksius di seluruh dunia. Kajian ini dijalankan dari 4 September 2012

sehingga 31 Ogos 2013 di dalam rumah tumbuhan di USM. Terdapat tiga objektif utama

kajian ini; untuk mengkaji kitaran hidup kedua-dua spesies tumbuhan, untuk mengkaji

persaingan di antara kedua-dua spesies tumbuhan dan untuk mengkaji tahap toleransi

tumbuhan kajian terhadap saliniti. Kedua-dua spesies tumbuhan kajian diambil dari

dalam tangki tumbuhan air di Pusat Pengajian Sains Kajihayat dan kemudian

dibersihkan serta ditimbang bagi mendapatkan bacaan berat basah. Kedua-dua spesies

tumbuhan ditanam di dalam bekas yang berukuran 33.5 cm x 22 cm x 11.5 cm dimana

masing-masing mempunyai enam replikat. Untuk kajian kitaran hidup dan

persaingan tumbuhan, gambar untuk setiap perubahan bentuk tumbuhan telah

diambil serta kadar pertumbuhan bagi setiap pokok direkodkan setiap hari. Bagi

tujuan mengkaji tahap toleransi tumbuhan terhadap saliniti, 50 g tumbuhan ditanam

di dalam bekas yang mengandungi air laut pada kepekatan yang berbeza dan setiap

perubahan dicatatkan setiap hari. Daripada kajian kitaran hidup, Pistia stratiotes

dilihat berkemampuan untuk membiak secara penghasilan biji benih dan vegitatif

manakala Salvinia molesta pula hanya membiak secara vegitatif pada keseluruhannya.

Selain itu, dalam kajian persaingan, Salvinia molesta telah menyaingi Pistia stratiotes

dengan nisbah 9:1, Salvinia kepada Pistia. Untuk kajian tahap toleransi tumbuhan

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terhadap saliniti pula Salvinia molesta telah direkodkan mampu untuk bertahan di

dalam air laut yang berkepekatan 25% manakala Pistia stratiotes langsung tidak mampu

untuk bertahan di dalam keadaan air laut. Usaha untuk kita mengenali setiap kelakuan

tumbuhan adalah penting dan merupakan langkah pertama bagi kita mengawal

pertumbuhan pokok-pokok ini sebelum ia membiak sehingga ke tahap yang menganggu

dan mengancam keadaan persekitaran. Memandang tumbuh-tumbuhan ini mampu untuk

membiak secara agresif, kajian mengenai tumbuh-tumbuhan ini amatlah penting dalam

usaha-usaha kita untuk menjaga alam sekitar serta sumber air kita yang utama seperti

kolam, tasik, mahupun sungai.

xiii

A COMPARATIVE STUDY BETWEEN Pistia stratiotes L. AND Salvinia

molesta MITCH. BASED ON LIFE CYCLE AND SALINITY TOLERANCE

ABSTRACT

The aim of this study was to investigate the competition between two floating aquatic

weeds; Pistia stratiotes and Salvinia molesta which are listed as the most noxious

aquatic weeds worldwide. This study was carried out from 4 September 2012 until

31August 2013 in the plant house at USM. There were three main objectives of this

study; to examine the life cycle of both plant species, to examine the competition

between the two plant species and to examine the level of plants tolerance towards

the salinity. Both studied plant species were adopted from the water plant tank in the

School of Biological Sciences and which then were cleaned and weighed to obtain

the wet weight readings. Both plant species were grown in containers measuring 33.5

cm x 22 cm x 11.5 cm where each plant has six replicates. For the life cycle and

plant competition study, any plant changes in the form of images were taken and the

growth rates for each plant were recorded daily. For the level of plants tolerance

towards the salinity study, 50 g plant was grown in containers containing seawater at

different concentrations and any changes in plant were recorded daily. From the life

cycle study, Pistia stratiotes was capable of reproducing through seeds germination

and vegetative reproduction while Salvinia molesta can only reproduce vegetatively.

Moreover, in term of competition study, Salvinia molesta had outcompeted Pistia

stratiotes with the ratio of 9:1, Salvinia to Pistia. For the level of salinity tolerance

study, Salvinia molesta was recorded to be able to survive in the seawater with

concentration of 25% meanwhile Pistia stratiotes was not able to survive in seawater

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at all. The attempt for us to know each plant behaviour are essential and it is the first

step for us to control the growth of these plants before they multiply to such an

extent that interferes and threaten the environment. Since these plants are able to

grow aggressively, the study of these plants is vital in our efforts to protect the

environment and our water resources such as ponds, lakes, or rivers.

1

CHAPTER 1

GENERAL INTRODUCTION

1.1 Introduction

Based on ISI Web of Knowledge index, out of 1,512 studies on aquatic weeds

worldwide there were only five intensive studies focusing on the ecology of floating

aquatic plant. These studies were conducted by Walsh et al. (2013), Galatowitsch

(2006), Adams et al. (2002), RuizAvila and Klemm (1994) and Harper et al. (1990).

In addition, based on available literatures there were approximately 235 species of

aquatic plants in the aquatic ecosystems of Malaysia (Burkill, 2002).

Lately, the increasing number of invasions by alien species or non-native

species was reported to affect the habitats around the world (Vitousek et al., 1997).

Non-native plant species affect negatively the local plant community composition,

ecosystem functions and human uses. Furthermore, most of the non-native species

are failed to successfully establish, but some of the species are able to grow and

colonise a certain area to nuisance levels (Chapin et al., 2000).

Aquatic plants are widely distributed in any water body ranges all over the

world. Ten years of field surveys were carried out by Mansor (1996) on various

water bodies, rivers, streams and canals in Malaysia. This study covered 28 rivers

and five lakes of Peninsular Malaysia, Sabah and Sarawak. Throughout these survey,

Mansor (1996) stated that there are four problematic floating aquatic weeds in

Malaysia; namely Eichhornia crassipes, Salvinia molesta, Pistia stratiotes and

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Lemna perpusilla. The favourable tropical climate and conducive environment of

Malaysia had triggered the massive growth of these weeds.

A study by Marwat et al. (2011) from 2005 until 2007 in Dera Ismail Khan

District of KPK, Pakistan found that floating weeds have caused serious problems,

however they are used for various purposes. The latest research on the invasive alien

in Italy was done by Brundu et al. (2012) and stated that Pistia stratiotes and

Eichhornia crassipes are invading Campania and Sardinia. These two floating

hydrophyte invasions consumed high cost of mechanical removal works and

unsuccessful to be utilized in the long term. The introductions of exotic species is

one of many factors contribute to the presence of these plants as ornamental plant

and used as phytoremediation. A suggestion for the importance of regulation in the

trade sector towards the invasive plant species and a set up of national strategy draft

on these biological invasions are the priority for Italy. In addition, several specific

action plans for aquatic plant species and surrounding habitats, as in the case of

inland waters, are also may be required.

Study and documentation on aquatic plant species today, especially free

floating plants are still limited and insufficient for reading materials. More research

was focused on Eichhornia crassipes from Pontederiaceae family and little were

done on other family (Perna et al., 2012). Intensive research on plant anatomy, plant

morphology, plant taxonomy, life cycle, and origin of aquatic plant is needed to

supply information for the researcher. From these studies, it is possible to estimate

the biodiversity of a given area and further conservation work on that area could be

done. As conservation has becomes more politically important, plant identifications

works impacts not only on the scientific community, but society as the whole

(Knapp, 2010).

3

It should be noted that not only in Malaysia but the whole world are facing

the problems with floating aquatic plant species. Intensive observation is crucial to

build knowledge and information not for our society alone but it should be done

globally. Since the growth and development of this type of aquatic plant species is

connected to water body, it should be handled seriously because water is the base of

every living thing and we need to secure our water resources.

4

1.2 Objectives of study

There are three objectives of this study as listed hereby:

1. To study the life cycle of two free floating aquatic plant species, Pistia

stratiotes and Salvinia molesta.

2. To observe the competition between Pistia stratiotes and Salvinia molesta.

3. To observe the physiological responses of Pistia stratiotes and Salvinia

molesta under varying degree of salt tolerance, by applying seawater at

different salinity.

5

CHAPTER 2

LITERATURE REVIEW

Aquatic ecosystem is an ecosystem surrounded by water. Organisms that

form communities are depending on the environment and interact with each other.

Marine ecosystems and freshwater ecosystems are the two main types of aquatic

ecosystems (David and Rhodes, 1999). Numerous important environmental functions

that performed by aquatic ecosystems such as recycles the nutrient through water

cycle, purifying the water source, debilitate floods, revitalize the ground water and

equip the habitat for wildlife (Solan et al., 2004) and aquatic ecosystems play for

human recreation and are very important spot for tourism.

Lately, the health of aquatic ecosystems had been disturbed by various stress

results from the human activities, and environmental changes (Keddy, 2010).

Stresses on an aquatic ecosystem can be results by the alterations of the environment,

either through the physical, chemical or biological changes. Physical alteration

includes changes in temperature of the water, water movement and light availability,

while chemical alteration includes changes in the bio-stimulatory nutrients loading

rates, oxygen consuming materials and toxins. Biological alteration includes the

exotic species influx and over-harvesting of commercial species. With the increasing

in human populations, excessive stresses on the aquatic ecosystems could be

imposed. The usage of synthetic detergent found to kill the aquatic organisms even in

a small amount and effect the local environment. Based on a study, six hours

exposure of synthetic detergent can kill 70% of aquatic life (Wan Abdullah, 1995).

6

The alteration of aquatic life forms might collapse the food chain of aquatic and land

food web.

Approximately, 71% of the Earth‟s surface is covered by marine ecosystems

and it contain for about 97% of the planet‟s water. 32% of the world‟s net primary

production is generated by marine ecosystems. Since the presence of dissolved

compounds, especially salts in the marine water, they are distinguished from

freshwater ecosystems. Eighty five percent from seawater estimated that the

dissolved materials are sodium and chlorine. The average salinity of seawater is 35

parts per thousand (ppt) of water and this number may be varies among different

marine ecosystems (Pinet, 1996). Whereas, freshwater ecosystems cover 0.80% of

the Earth‟s surface and inhabit only 0.009% of its total water. Three percent of net

primary productions have been generated from freshwater ecosystems. 41% of the

world‟s known fish species comes from freshwater ecosystems. There are three basic

types of freshwater ecosystems; wetlands, lentic and lotic. Wetlands are areas where

the soil is saturated or inundated for at least part of time. Lentic ecosystem is a slow

moving water body including pools, ponds and lakes. Next, lotic ecosystem is a

faster moving water body, such as streams and rivers (Wetzel, 2001).

2.1 Aquatic Plant

Each of aquatic ecosystems stands in need of aquatic plants because they play

a major role by providing food and habitat to aquatic organisms such as fish and

wildlife. Plants stabilise sediments, improve water clarity and add diversity to the

shallow areas of lakes (Madsen, 2009). Aquatic plants grow completely or partially

in water. They are also known as macrophytes or hydrophytes, can be found in the

7

shallow zones of lakes or rivers. This shallow zone is called as littoral zone which is

shown in Figure 2.1. This zone receives sufficient light penetrations to the bottom to

support the growth of plants.

There are three groups of plants that grow in littoral zones. Emergent plants

inhabit the shallowest water with their roots in the sediment and their leaves are

extending above the water surface. Common reed, spike rush and cattail are the

representative species of emergent plants (Mashhor et al., 2002). Floating-leaved

plants grow at intermediate depths and some of this species are rooted in the

sediment. Water lily is in this group. While others are free floating with roots that

hang unanchored in the water column. Water lettuce and water hyacinth are the two

examples of free floating aquatic plants (Haller, 2009). Plants that grow their stems

and leaves entirely underwater are known as submerged plants. Submerged plants

display a wide range of plant shapes and grow from near shore to the deepest part of

the littoral zone. Submerged plant species are including Hydrilla, Cabomba and

Egeria (Haller, 2009).

Figure 2.1: The three primary zones of a lake (Source: Ruth, 2010)

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2.1.1 The Benefits of Aquatic Plant

Aquatic plants are essentials components of healthy aquatic ecosystems.

Plants, whether on land or in or around water photosynthesize using sunlight, carbon

dioxide and water to grow, produce new plant tissue and grant us with oxygen

through this process. Aquatic plants also play important roles in the aquatic

environment (Madsen, 2000). Microscopic plants (algae) or phytoplanktons are

essential elements which form the base of aquatic food chain. Aquatic macrophytes

provide ideal habitats for big fish and shelter for juvenile fish, organisms as fish food

and also provide food for insects, waterfowl and other wildlife. Since all plant,

including those that grow underwater produce oxygen after photosynthesis process

occur, they are the major source of oxygen for aquatic animal life (Bonvechio and

Bonvenchio, 2006).

Rooted plants stabilize shorelines and bottom sediments. They absorbs

nutrients and filter pollutant from runoff, which improve water purity. A diverse

aquatic plant population adds beauty to the water body. Many people recognize and

appreciate the aesthetic value of aquatic vegetation, whether in the backyard

fishpond, around the retention pond, or along the shoreline of a lake (Lembi, 2009).

Furthermore, the developing technology in producing bio-fuel from the aquatic plant

biomass is becoming a major concern nowadays. With consideration of raw material

constitutes 40 similar to 80% production costs of bio-fuel, this bio-fuels are made

from volatile fatty acids which is derived from waste biomass of aquatic plants has a

potential to offers significant economical advantages (Chang et al., 2010).

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2.1.2 Problems Rises from Excessive Aquatic Plant

Unfortunately, non-native plants that are introduced to new habitats often

become a nuisance by hindering human uses of water and threaten the structure and

function of diverse native aquatic ecosystems. Simply characterised, invasive plants

are those species that easily to prevail over geographic and environmental barriers,

fast self establishment, and then expand their numbers and ranges rapidly in the new

habitat (Richardson et al., 2000). They are often extirpating or displacing populations

of indigenous species in this invasion process.

Plants that have been introduced into new regions, either deliberately or

inadvertently, by human activities are the highly successful plant invaders (Mack and

Lonsdale, 2001). For example, at least 128 of the approximately 5,800 crops or

ornamental plants introduced intentionally into the United States have become

noxious weeds (Pimentel et al., 1989). The most commonly found commercial

species was Indian hygrophila (Hygrophila polysperma (Roxb.) T. Anderson) later

followed by water hyacinth and branched bur-reed (Sparganium erectum L.).

Misidentification of the plant and inability to recognize the invasive species and also

the ignorance of the messages from the websites by many of the hobbyists had

becoming the major problem. Much of wetland managers, aquatic plant nursery

representatives and dealerships have inadequate knowledge of the aquatic plants that

they sell. Leading candidates for this dubious distinction are the floating weeds

Eichhornia crassipes, Pistia stratiotes, and Salvinia sp.; submerged weeds

Ceratophyllum demersum, Egeria sp., Hydrilla verticillata, Myriophyllum sp., and

Potamogeton pectinatus; rooted, shallow-water plants such as Ludwigia sp.,

Polygonum sp., Typha sp.; several grass species, and some wetland shrubs and trees

(Charudattan, 2001).

10

To manage these infestations of aquatic weeds, various significant resources

are often expended because unchecked growth of these invasive species often

interferes with the use of water. This aquatic vegetation could be considered as

harmful when its notable growth causes problems for the use of ecosystems, such as

navigation, water sports, and fishing activities. The invasive aquatic plant species

which affecting the native aquatic plant species, resulting in the need for the

controlling methods implementation or management. This marked growth of aquatic

vegetation also increases exposure to flash flooding and result in threatened public

health conditions (Kay and Hoyle, 2001).

Upon from uncontrolled growth of various aquatic vegetation species in some

watersheds, several studies have been conducted with the aim to understand the

biology (Antuniasi et al., 2002) and the distribution (Cardoso et al., 2002), as well as

the plan for management of these species which have assumed holding the status of

weeds (Cavenaghi et al., 2003).

The three most notorious weeds, Eichhornia crassipes (water hyacinth),

Pistia stratiotes (water lettuce) and Salvinia molesta (giant salvinia) cause serious

problem in nearly all countries, affecting almost all uses of water bodies such as for

aquaculture, commercial and subsistence fishing, drinking and household

consumption, hydropower generation, irrigation, transport and recreation

(Charudattan, 2001). By replacing the native flora and fauna, these weeds would

affect biodiversity and often causing irreversible changes to habitats. With the

increase of mosquitoes breeding sites, it would also increase in the insect-borne

human diseases count. Another important concern which potential to affect the

recreation and tourism is the loss of aesthetic value of waterfront communities due to

11

weed growth. Sedimentation and eutrophication rates will be increased from the dead

biomass of large weed and reduces water depth. Floating weeds cause problems by

partially or completely forming a thick blanket in large and small water bodies,

interfering with the normal access of water. They increase water loss from any water

body through the dual actions of evaporation and transpiration (Janes et al., 1996).

With the evapotraspiration process two times faster than normal, the lake will

quickly become shallow. If not treated and managed properly, the man-made lake

will not function anymore (Mansor, 1994). Dense mats of aquatic macrophytes, both

canopies of free floating species and the sub-canopy species distinct the littoral zone

with lower DO concentrations and pH (Frodge et al., 1990).

Intensive fisheries industry often involves adding large amounts of

commercial feeds and inorganic fertilizers into ponds. Nutrients introduced into the

water through feeds and fertilizers often create an ideal environment for aquatic

weed growth. Submerge aquatic weeds are particularly undesirable because fish

harvesting nets will ride up over the weeds and allow fishes to escape. Pond with

highly weed infestations can be impossible to harvest since the weight of the weeds

accumulating in the seine can become too great to be pulled (Shelton and Murphy,

1989). In their impact on human society, invasive plants charge economic, social,

and medical costs in a number of ways. They compete with food and fiber crops,

ornamentals, and other aquatic plants for nutrients and sunlight. They also interfere

with water management in agriculture by infesting irrigation ditches and other

waterways; reduce incomes from recreational hunting and fishing, and from tourism;

restrict access to foreign markets (Culliney, 2005).

For example, Salvinia molesta is a free floating aquatic fern native to South

America, spreading throughout the tropics and subtropics over half of the twentieth

12

century. The ability to grow very quickly and a dense mats forming over lakes and

slow moving rivers could cause wide range of ecological problems and devastating

economic loss (Ali et al., 2011). For examples, mats of Salvinia could block the use

of waterways from the commercial and recreational purposes and degrade the

aesthetics value of waterside (Johnson et al., 2001). Mats of Salvinia reduce habitats

for some birds‟ species, limit the access way to a fishing area and probably revise

with fisheries, all with negative economic impacts. It also interfere by clog the water

intakes of agriculture irrigation, water stock and electrical generation dam (Bravo et

al., 2012). In some reports, it provides habitats for human diseases vector with

serious socioeconomic consequences (Hussner et al., 2010). Salvinia molesta dense

mats provide ideal habitats for Mansonia mosquitoes, rural elephantiasis principal

vector and other mosquitos‟ species which is responsible for the transmission of

encephalitis, dengue, and malaria (Kweka et al., 2012). In developing countries, the

mats of Salvinia could cause a devastating impact on the use of waterways for

transportation, farm lands, and towards communities which depends on fish for local

consumption. This species is also known as a weed of paddy field that alters the

production by competing for nutrient, water and space (Sinhababu et al., 2013).

Flora and fauna depends on open water body to receive sunlight, oxygen and

space for nourishment and growth, nest construction, and mating. So, mats of aquatic

vegetation could lower the oxygen concentration in the water, necessary for the flora

and fauna survivorship (Cilliers et al., 2003). Moreover, reducing of sun penetration

and oxygen concentration may inhibit the photosynthesis of submerge plant, make

the water body high in the carbon dioxide and hydrogen sulphide concentration

which will choke out other living organism in the water ecosystems (Richardson and

Wilgen, 2004).

13

As well as Salvinia molesta, a dense mat of Eichhornia crassipes could

reduce the light penetration to submerged plants, thus diminishing oxygen supply in

the aquatic community (Martins et al., 2008). It gives result in the lacking of

phytoplankton densities, hence affecting the fisheries industry by altering the

invertebrate community‟s composition (Turpie et al., 2003). Water hyacinth often

disturbing and destroy native flora and fauna habitats by competes with the native

plants, displacing wildlife habitat and forage (Henderson, 2001). Hanging roots of

water hyacinth also traps moving sediment, combine with detrital production and

siltation under water hyacinth mats results in higher sedimentation loading (Nel et

al., 2004). Furthermore, water hyacinth infestation management through mechanical

harvesting or herbicidal treatment will cause damages to nearby desirable vegetation

such as ornamental plants (Higgins et al., 2001).

According to Stuckey and Les (1984) in Florida, Pistia stratiotes or water

lettuce is one of this invasive floating aquatic weed. Infestation of water lettuce mats

able to block navigational channels, impedes water flow in flood control canals and

irrigation canals, and disrupting submerge flora and fauna, recorded since 18th

century before. Just like water hyacinth, roots of water lettuce, composed of long

adventitious roots aligned with extensive lateral rootlets. These extensive infestations

accelerate siltation rates as they begun to slow the water velocities in rivers or

streams. Consequently, benthic substrates degradation under water lettuce mats

resulted in creating unsuitable habitats and nesting sites for many kind of fish

species, as well as macroinvertebrate (Görgens and Wilgen, 2004). Likewise, water

lettuce has the ability to bioaccumulate noticeable amounts of heavy metals, so the

detritus under the water lettuce mats could be highly toxic (Sridhar, 1986).

14

The total cost imposed solely by invasive aquatic weeds in the United States

was estimated to range from $900 million to $14 billion annually (Rockwell, 2003).

The Economic Cost of Invasive Non-Native Species to the British Economy suggests

that invasive species cost £1.7 billion every year, which includes £251 million in

Scotland. For example, with water primrose, a group of South American aquatic

weeds which grow rapidly and can block waterways it is estimated that the current

timely eradication will cost £73,000 which is significantly less than the estimated

£242 million that it would cost if the plant was to become widely established as it has

on the continent in countries like France and Belgium (Williams et al., 2010). They

have badly degraded more than 15 million ha of grazing lands and natural

ecosystems in Australia (Glanzing, 2003). Noxious weeds have invaded an estimated

10 million ha in South Africa (van Wilgen et al., 2001). This is a critical loss of a

resource vital for economic growth. Clearly, invasive plants take an unacceptable toll

on agriculture and other sectors of the economy.

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2.2 Studied Plant

2.2.1 Pistia stratiotes L.

The name Pistia stratiotes L., an unique aroid comes from the Greek “pister”

meaning hollow trough, in the sense of a drinking through (Mayo et al. 1997) or the

Greek “pistos” meaning water, and “stratiotes” meaning soldier (Yates, 2005). It was

classified in 1943 to its own Pistiaceae, but as a result of later research it is now in

the Araceae, subfamily Aroideae, tribe Pistieae, and is the only species in the genus

Pistia. It is a perennial monocot of the Araceae family. Pistia stratiotes is also

known as water lettuce, water cabbage, Nile cabbage or shellflower.

Pistia stratiotes, or water lettuce is an interesting, unique aroid. Glazier

(1996) describes P. stratiotes as a free-floating perennial of quiet ponds. It is

stoloniferous, forms colonies, and has rosettes up to 15cms across. The illustration of

Pistia stratiotes is shown in Figure 2.2. It has long, feathery, hanging roots. Its leaves

are obovate to spathulate-oblong, truncate to emarginate at the apex, and long-

cuneate at the base. Leaves are light green and velvety-hairy with many prominent

longitudinal veins. Inflorescences are inconspicuous and up to 1.5cms long. Flowers

are few, unisexual, and enclosed in a leaf-like spathe. The spathe generally shows a

constriction between the groups of flowers male and the female. The spathe below

the constriction opens first in the morning hours to expose the wet stigma, whereas

the male flower remains enclosed. Some hours later, the spathe opens completely and

exposes the part bearing male flowers (Neuenschwander et al., 2009). The

inflorescence of this plant is shown in Plate 2.1. Water lettuce does reproduce by

sexual and vegetative means. When stolons grow from the mother plant, new

daughter plants will be formed and known as seedlings in matured plant.

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Stolon

Figure 2.2: Illustration of Pistia stratiotes (Source: IFAS, 1990)

Plate 2.1: Inflorescence of Pistia stratiotes (in the red circle)

17

Like any potential invasive species, Yates (2005) also describes that it must

be kept in check so it does not become destructive; however, it has valuable

properties, as a medicinal, a food source, and environment remediator. There is some

confusion about the origin of water lettuce due to its worldwide distribution;

however, there is strong evidence that it is native to South America. P. stratiotes is

now found throughout the tropics and subtropics and is one of the most widely

distributed hydrophytes in the tropics (Holm et al., 1977). The map on the

distribution of P. stratiotes is shown in the Figure 2.3. P. stratiotes is a popular

garden pond plant and is often spread by the dumping of aquarium or ornamental

pond plants. It is a free-floating plant that is capable of forming dense mats on the

surface of lakes. Fragments or whole plants can spread via boats or fishing

equipment from an infested area to a clean body of water. According to Rivers

(2002), P.stratiotes can cause a severe impact on the environment and economy of

infested areas. The dense mats create by connected rosettes of the plant lead to the

majority of problems encountered with water lettuce. These mats can drive a

negative economic effect by blocking waterways, thus increasing the navigation and

hindering flood control efforts. Mats of P. stratiotes can also disrupt natural

ecosystems. They can lead to a lower concentration of oxygen in covered waters and

sediments by blocking air-water interface and root respiration, even extremely thick

mats of P. Stratiotes can prevent sunlight from reaching underlying water. The

cumulative effect of these negative characteristics of the plant is loss of biodiversity

in invaded habitats. P stratiotes continues to be sold through aquarium supply dealers

and through the internet (Ramey, 2001).

In a published study, Pimentel et al. (2000) determined invasive aquatic

plants species costs $ 10 million in losses and damage and $100 million in control

18

costs in the US. Later in 2002, Dray Jr. and Center estimated expenditures increased

to over $1 million dollars annually in Florida by 2002. Although, there are several

other aroids considered invasive in various regions, P. stratiotes is by far the most

insidious one. According to Pimentel et al. (2005) P. stratiotes among several

invasive aquatic plant species, is altering fish and other aquatic rivers and lakes.

1 mm

5 mm

19

Figure 2.3: Phytogeographic highlight of Pistia stratiotes L. in the world map. (Source: Evans, 2013)

Confirmed ·~non-native

•'

Seeds iri ----~..,_

paleo-sediments (-2,2408P)

'·. ·~ ..

· .. ~~~ · • •. • High diversity of

specialist herbiVore.s

'

~.

0 2,500! 5,000

..........

·'

.. , . ~'~\

~ . ' \", ·confirmed non-native

l 1·· ;

~, J f.'

, ··.:_ Likely center II of origin for Pistia clade ~ · · (-85 Mya)

• 10,000 Km

Gray shaded area denotes approximate current range for Pistia stratiotes L. Map constructed from ources noted in tl1e primary text

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2.2.2 Salvinia molesta

Salvinia molesta is a free floating aquatic fern. It produces a horizontal

rhizome lies under water and two types of frond, buoyant and submerged. The

mature plant produces egg-shaped spore sacs or sporocarps, containing infertile

spores as can be seen in Figure 2.4. It lacks true roots but its submerged fronds

function as roots. On their upper surface they have rows of cylindrical papillae. Each

papilla has four hairs at its distal end that are joined together at their tips to form

what looks like an inverted egg-beater. The cage-like structure of the end hairs is an

effective air trap giving the plant buoyancy in the water. The structure of Salvinia

molesta papillae are shown in Plate 2.2. The papillae, end hairs and upper surface of

the plant are water repellent in comparison to the under surface of the leaf, which

attracts water. It is this difference in water attraction that maintains the correct

orientation of the plant on the water surface. The fronds are light to medium green,

often with brownish edges in mature plants, and with a distinctive fold in the center.

The plant exhibits great morphological variation depending on the conditions of

habitat such as space and nutrient availability, and ranges from a slender floating

specimen with leaves less than 1.5cm wide to one with leaves up to 6cm wide

(Pieterse et al 2003).

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Figure 2.4: Illustration of Salvinia molesta (Source: IFAS, 1990)

Plate 2.2: Cage like structure of Salvinia molesta papillae (in the red circle)

1 mm

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Salvinia molesta is a floating aquatic fern that thrives in slow-moving,

nutrient-rich, warm, freshwater. The map on the distribution of Salvinia molesta is

shown in the Figure 2.5. A rapidly growing competitive plant, it is dispersed long

distances within a water body (via water currents) and between water bodies (via

animals and contaminated equipment, boats or vehicles). Salvinia molesta is

cultivated by aquarium or pond owners and it is sometimes released by flooding, or

by intentional dumping. Salvinia molesta may form dense vegetation mats that

reduce water-flow and lower the light and oxygen levels in the water. This stagnant

dark environment negatively affects the biodiversity and abundance of freshwater

species, including fish and submerged aquatic plants. Salvinia molesta can alter

wetland ecosystems and cause wetland loss and also poses a severe threat to socio-

economic activities dependent on open, flowing and or high quality water bodies,

including hydro-electricity generation, fishing and boat transport (Chamier et al.,

2012).

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Figure 2.5: Countries where Salvinia molesta has been a serious problem in the fresh water systems. (Source: Forno and Harley, 1979)

* Origin of Salvinia molesta and Cyrtobagous salviniae

• Salvinia molesta under biological control

• Salvinia molesta not under control

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CHAPTER 3

THE LIFE CYCLE OF Pistia stratiotes AND Salvinia molesta

3.1 Introduction

Like other floating plants, Pistia stratiotes has a notable capacity to build up

biomass rapidly (Reddy and De Busk, 1984). Pistia stratiotes debris was also used as

a biosorbent material to remove metals derived from industrial activities (Miretzky et

al., 2006) and the living plant is on demand to clear biological waste of water

treatment plants (Koné et al., 2002; Zimmels et al., 2006) or poluted ponds

(Vardanyan and Ingole, 2006). Chen et al. (2006) stated that Pistia stratiotes is also

used to reconstruct wetlands or to monitor water quality in rivers.

In most natural situations, Pistia stratiotes is a weed because it can quickly

overgrow and cover still-water surfaces in a shortest time. Like other floating water

weeds, it impedes fishing activities, boat traffic, and flood control, and mats of Pistia

can threaten hydropower generation dams. By covering water surfaces, it affects

habitats and biodiversity (Chamier et al., 2012). It blocks out sunlight, affecting

native water plants to reduce oxygen movement and thus either displaces or kills

native organisms, such as fish.

Consequently, heavy Salvinia molesta infestations have negative impact in

term of socio-economic because of their potential to ruin industries which depends

on clean water bodies. Salvinia is also may infest rice fields cultivating area,

irrigation channels or entrance to electricity generation stations; hence affect the

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